1. Field of the Invention
The present invention relates to a battery discharge control circuit and, more specifically, to a battery discharge control circuit to be incorporated into a battery discharger or a battery discharger combined with a battery charger to detect the charged state of a battery and to discharge the battery when the battery is not discharged.
2. Description of the Prior Art
Forced discharge of a battery by a battery discharger to cancel the memory effect of the battery needs caution against overdischarge. The battery discharger detects the terminal voltage V.sub.b of the battery, discharges the battery according to the discharged state of the battery and decides if the battery is discharged. As shown in FIG. 5, when a nondischarged battery, for example, a Ni--Cd battery (nickel-cadmium battery) having a rated voltage of 6 V and a terminal voltage of 5 V or above, is loaded into a battery discharger, the battery discharger starts discharging the battery automatically in a constant-current discharge mode or a constant-resistance discharge mode and stops discharging the battery upon a decrease of the terminal voltage V.sub.b below about 5 V and a decrease of the discharge current I.sub.D to zero. The battery discharger may be provided with a discharge start button and the battery discharging operation may be started by pushing the discharge start button.
The battery discharger that judges the discharged state of the battery simply from the terminal voltage V.sub.b of the battery is unable, in some cases, to judge the discharged state of the battery correctly because the terminal voltage V.sub.b of the battery is dependent on the self-healing characteristic and temperature characteristic of the battery. If the battery discharger is unable to discriminate correctly between the discharged state and the nondischarged state, the terminal voltage V.sub.b of a battery in a nondischarged state loaded into the battery discharger increases and the state of the battery becomes a discharged state or the state of the battery becomes a discharged state after the battery has completely been discharged, so that discharge starting time and discharge frequency are indefinite.
Furthermore, when a battery is loaded into a battery discharger that starts discharging the battery automatically upon the reception of the battery therein, it occurs sometimes that battery discharger is unable to detect the terminal voltage V.sub.b of the battery correctly due to noise generated by chattering contact action between the battery and the battery discharger in loading the battery into the battery discharger.